Selective catalysis



United States Patent Ofiice 3,535,398 SELECTIVE CATALYSIS Nai Yuen Chen,Cherry Hill, and Stanley J. Lucki, Runnemede, N.J., assignors to MobilOil Corporation, a corporation of New York No Drawing. Filed Mar. 2,1966, Ser. No. 531,045 Int. Cl. C07c /02, 11/00 U.S. C]. 260-677 3Claims ABSTRACT OF THE DISCLOSURE This invention relates to a novelprocess for the selective conversion of certain organic compounds from amixture of the same with other reactants. More particularly, the presentinvention is directed towards a novel selective conversion processutilizing ditferences in rates of sorption by crystallinealuminosilicates of various organic compounds.

The use of aluminosilicates to achieve selectivity between a mixture ofvarious compounds based on differences in molecular shape or size iswell known in the art. Thus, for example, an early development in thisarea involved the use of crystalline aluminosilicates, commonly referredto as molecular sieves, to effect a simple physical separation of amixture of organic compounds which differed in molecular dimensions.

Various processes of this general type have been proposed for treatingmixtures or petroleum fractions containing branched-chainandstraight-chain hydrocarbons, by selectively adsorbing the straight-chainhydrocarbons therefrom, employing adsorbents which selectively adsorbthe straight-chain compounds to the substantial exclusion of thebranched-chain compounds. To achieve such separation, molecular sieveshave been employed for effecting physical separation of mixtures ofmaterials of varying molecular size. Such substances have been describedby Barrer in several publications and in US. 2,306,610 and US.2,413,134. Thus, molecular sieves are essentially the dehydrated formsof crystalline natural or synthetic hydrous siliceous zeolitescontaining varying quantities of sodium, calcium and aluminum with orwithout other metals. All or a portion of the sodium or calcium ionsnormally contained in the molecular sieve structure may be zeoliticallyreplaced with a number of various other ions. The atoms of sodium,calcium or metals in replacement thereof, silicon, aluminum and oxygenin these zeolites are arranged in the form of an aluminosilicate salt ina definite and consistent crystalline pattern. This structure contains alarge number of small cavities, interconnected by a number of stillsmaller holes or channels. These cavities and channels are preciselyuniform in size. Chemically, these zeolites may be represented by thegeneral formula:

where Me is a metal cation, x/n is the number of exchangeable cations ofvalence n, x is also the number of aluminum atoms combined in the formof aluminate, y

3,535,398 Patented Oct. 20, 1970 is the number of silicon atoms and z isthe number of water molecules, removal of which produces theadsorptivity of the zeolite. At the present time, various types ofmolecular sieves can be prepared, as more fully hereinafter discussed,designated as zeolites A, ZK4, ZKS, alpha, S, T and D, and the naturalzeolites chabazite, gmelinite and offretite having the aforementionedproperties are also available, and which are crystallinealuminosilicates having pores of about 5 A. in diameter.

Additionally, aside from effecting a mere physical separation,crystalline aluminosilicates have also been used to achieveshape-selective conversion between a mixture of various compounds basedon diiferences in molecular shape. In this connection, US. 3,140,322discloses and claims the selective conversion of at least two molecularspecies of differing shape utilizing crystalline aluminosilicates havinga pore size sufficient to admit one molecular species, either a reactantor product, to the exclusion of the other and effecting a chemicalconversion within said pores.

Thus, it can be seen that in the heretofore practiced processes, eitherphysical separation or catalytic conversion, involving selectivity withcrystalline aluminosilicates it was essential that a difference inmolecular shape between the reactants or products was present. Theentire basis for selectivity was predicated on the fact that the poresof an aluminosilicate would selectively admit some reactants or releasesome products to the substantial exclusion of others due to the factthat certain reactants or products had a molecular size or shape whichwas larger than the pore size of the crystalline aluminosilicate.

It should be immediately obvious that although the above-describedprocesses were very elfective in accomplishing their respectiveobjectives, their use was limited to those situations involving amixture of reactants which differed as to molecular dimension. It shouldalso be readily apparent that many situations exist wherein selectivityis desired from a mixture of reactants which all have approximately thesame molecular diameter.

Accordingly, it is the primary object of this invention to provide anovel process for effecting selective catalytic conversion of certainorganic compounds from a mixture of reactants wherein all reactants havea molecular dimension such that they can enter the internal cavities ofan aluminosilicate having a pore size of about 5 angstrom units.

The novel process of this invention is based on the fact that althoughcompounds which have molecular dimensions such that they can enterwithin the pores of an aluminosilicate, their rate of sorption by thealuminosilicate will vary depending upon many factors including thespecific nature of the compound. Thus, for example, in a reactionmixture containing the materials A and B which would normally reactcatalytically to give the respective products A and B, it is possible toselectively provide only for the reaction A-aA' if, in fact, the rate ofsorption of A by the aluminosilicate is far greater than the rate ofsorption B so that A will enter the pores of the aluminosilicate and beconverted to A. It will be immediately noted that in the above examplethe molecular diameter of B is such that it is not prevented fromentering the pores of the aluminosilicate, but the selectivity of theinstant invention is due to the fact that B enters the pores of thealuminosilicate far more slowly than A so that A can enter and bechanged to A in a selective manner.

The process of the instant invention is particularly adapted to theseparation of straight-chain polar compounds from mixtures of the samewith straight-chain nonpolar compounds, as well as the separation ofcis-isomers from trans-isomers. Thus, in accordance with the novelteachings of this invention, it is possible to separate polar compounds,i.e. carboxylic acids, organic phosphorus containing compounds, organicsulfur containing compounds, nitriles, organo nitro compounds,aldehydes, ketones and esters having a diameter of about Angstrom unitsor less from mixtures of the same with nonpolar straight-chain compoundshaving a molecular diameter of about 5 Angstrom units or less, i.e.hydrocarbons such as pentane, hexane, butane, butene, heptene, etc.

In like manner, the novel process of this invention can be employed toeffect selective conversion of cis and transisomers, i.e. cis-butene-2from trans-butene-2 and cis-1,3- pentadiene from trans-1,3-pentadiene.As has heretofore been stated, selectivity is achieved not by virtue ofthe complete exclusion of one of the components from the catalytic sitescontained within the pores of the aluminosilicate, but by the differencein the rate of diffusion of the various isomers through the pores of thealuminosilicate.

The crystalline aluminosilicates employed herein for accomplishing theselective conversion indicated above, have pore size structures of about5 A. diameter and Si/Al ratios of at least about 1.0 and preferably ofat least 1.6. The crystalline aluminosilicates, contemplated for thepurposes of this invention include ZK4, ZKS, alpha, A, S, T and D typesand the natural occurring zeolites chabazite, gmelinite and offretite. Adescription and preparation of the ZK4 type crystalline aluminosilicate,as described above, is disclosed in application Ser. No. 134,- 841,filed Aug. 30, 1961, now Pat. 3,314,752. A description and preparationof the ZK5 type crystalline aluminosilicate is disclosed in applicationSer. No. 174,718, filed Feb. 21, 1962, now abandoned. A description andthe preparation of the alpha type crystalline aluminosilicate isdisclosed in application Ser. No. 237,289, filed Nov. 13, 1962, now Pat.3,375,205. A description and the preparation of the S type crystallinealuminosilicate is disclosed in Pat. No. 3,054,657, issued Sept. 18,1962. A description and the preparation of the T type crystallinealuminosilicate is disclosed in Pat. No. 2,950,952, issued Aug. 30,1960. A description and the preparation of the D type crystallinealuminosilicate is described in British Pat. 868,- 846 (series of 1960).The disclosures of the aforementioned pending patent applications andpatents are incorporated herein by reference and constitute part of thedisclosure of this application. It will be understood, of course, thatother types of crystalline aluminosilicates having a pore size structureof about 5 A. diameter and a Si/Al ratio of at least about 1.0 can alsobe employed in the novel method of the present invention.

A particularly preferred embodiment of this invention involves the useof crystalline aluminosilicates having a silicon to aluminum atomicratio of at least 1.6, especially when it is desired to effect selectiveconversion of polar straight-chain compounds from nonpolarstraight-chain compounds. For reasons not completely understood, it hasbeen found that in general aluminosilicates which have a silicon toaluminum ratio of at least 1.6 afford a far greater rate of sorption ofpolar straight-chain compounds than do aluminosilicates with a lowersilicon to aluminum ratio. As will be hereinafter set forth in theexamples, the relative rate of sorption of polar compounds byaluminosilicates having a silicon to aluminum ratio of at least 1.6 canvary up to a thousand times that by an aluminosilicate having a siliconto aluminum ratio less than 1.6, i.e., Zeolite A.

An important feature of the method of this invention is the provision ofsuitable catalytic activity within the intracrystalline structure inconjunction with the catalytic reaction system desired, although it isto be understood that the alumino-silicate might intrinsically have thedesired catalytic activity.

Catalytically active materials may be introduced into the crystallattice by suitably contacting the zeolitic solids with solutionscontaining catalytically active components such as zinc, cobalt, nickel,silver and others. In this manner, a catalytically active element can beintroduced by deposition of the incoming metal on the zeolitic solidafter drying the solution from the crystalline carrier. Often,establishment of catalytic centers can be effectively achieved byexchanging a portion of the metal ion of the aluminosilicate with an ionexhibiting catalytic activity for the desired conversion. Thus, forexample, a portion of the sodium or calcium ions normally contained inthe molecular sieve structure may be zeolitically replaced with a numberof various other ions such as silver, copper, aluminum, hydrogen, zinc,strontium, cobalt, gold, potassium, nickel, rare earths, ammonium,cadmium, mercury, lithium and magnesium. Replacement is suitablyaccomplished by contacting the molecular sieve with a solution of anionizable compound of the ion which is to be zeolitically introducedinto the molecular sieve structure for a sufficient time to bring aboutthe extent of desired introduction of such ion. After such treatment,the aluminosilicate is water-washed and calcined and thereafter is readyfor use.

The novel process of this invention is applicable for a wide variety ofselective conversion processes. Thus, for example, polar compounds canbe selectively cracked from a mixture of the same with normal aliphatichydrocarbons. Additionally, selective hydrogenation of polar compoundsfrom a mixture of the same with nonpolar straight-chain compounds can becarried out in accordance with the teachings of this invention. Thisinvention is also applicable for the selective hydrogenation oftransisomers from a mixture of the same with the correspondingcis-isomers. Other conversions wherein the novel process of thisinvention finds utility is for the selective halogenation of eitherpolar compounds or trans-isomers.

The following data and examples will serve to illustrate the novelmethod of this invention but it is not intended that it be limitedthereto.

EXAMPLES l-4 These examples will illustrate the relative rates ofsorption by aluminosilicates having varying silicon to aluminum ratios.

In these examples a one gram sample of a calcined synthetic zeoliteidentified as 5A having a silicon to aluminum ratio of 1 and a one gramsample of a calciumexchanged synthetic aluminosilicate identified asZeolite T and having a silicon to aluminum ratio of about 3.5

TABLE Relative rate of sorption (Zeolite I)/ (Zeolite A) ExampleCompound From the above examples, it can be seen that the silicon toaluminum ratio has a considerable effect on the rate of sorption ofvarious organic compounds.

EXAMPLES 5-10 These examples will also illustrate the effect of therelative rates of sorption of aluminosilicates as a function of siliconto aluminum ratio.

In these examples, a variety of calcium exchanged crystallinealuminosilicates having pores of about 5 Angstrom units in diameter werecontacted with a vapor of acetic acid and the amount of acetic acidsorbed was measured with the results shown in the following table.

TABLE Acetic acid sorbed,

t erweigh p Example Zeolite Si/Al cent Zeolite EXAMPLES 11-l3 6 EXAMPLE16 A mixture of n-hexane and l-nitropropane is contacted with a calciumexchanged crystalline aluminosilicate identified as Zeolite T atelevated temperatures in the order 800 F. Analysis shows that the moleratio of nhexane to l-nitropropane increased significantly due to thefact that the l-nitropropane was selectively cracked because of a vastdiflFerence in rates of sorption between n-hexane and l-nitropropane.

While preferred embodiments of the novel method of this invention havebeen described for purposes of illustration, it will be understood thatvarious modifications thereof which will be obvious to those skilled inthe art may be made without departing from the spirit of the invention.

What is claimed is:

1. A process for selectively hydrogenating unsaturated This exampleillustrates the selective chlorination of acetic acid from a mixture ofthe same with n-hexane.

A mixture of acetic acid, n-hexane and chlorine is contacted with acalcium exchanged crystalline aluminosilicate identified as Zeolite T ata temperature of about 350 C. After three minutes, the reaction isstopped and an analysis of the product shows that a substantial quantityof chloroacetic acid is obtained and an almost negligible quantity ofchlorohexane.

EXAMPLE Five grams of a catalyst identified as chabazite containingelemental platinum within its internal pore structure is contacted witha mixture of acrolein and n-butene in a shaker bomb and with hydrogen atan initial pressure of p.s.i.g. under constant agitation.

An analysis of the products obtained after the run was terminated showsthat the majority of the converted product was propionaldehyde withextremely little butane thereby demonstrating the selectivity of theprocess.

hydrocarbons in the presence of a crystalline aluminosilicate catalysthaving a silicon to aluminum ratio of at least 1.6, and a pore size ofat least 5 angstrom units and bearing within the interior thereofcatalytic sites which comprises contacting the same with at least twounsaturated hydrocarbon species having molecular diameters no greaterthan 5 angstrom units, at least one of which is capable of being sorbedwithin the internal pores of said aluminosilicate at a faster rate thanat least one other species, eflFecting a catalytic hydrogenation of themolecular species which has the greater rate of sorption so as toconvert the same to a hydrogenated species distinct from said admittedspecies and of a molecular shape capable of passing from the interior ofaid aluminosilicate.

2. The process of claim 1 wherein the reaction mixture comprises cis andtrans-isomers.

3. The process of claim 2 wherein trans-isomers are selectivelyhydrogenated.

References Cited UNITED STATES PATENTS 2,850,549 9/1958 Ray 260-6773,140,322 7/1964 Frilette et al. 260-667 3,267,023 8/ 1966 Miale et al.208111 2,866,835 12/1958 Kimberlin et al. 260-676 3,314,895 4/ 1967Munns 252455 HERBERT LEVINE, Primary Examiner US. Cl. X.R.

